An analysis of the work schedules of Great Barrier Reef pilots

Results and Discussion

5.8 Duration of Breaks between Work Assignments - Inner Route

As the minimum rest duration stipulated by the Australian Maritime Safety Authority varies depending on which shipping route is to be travelled, an assessment of the duration of breaks between work assignments on each of the three shipping routes in the Great Barrier Reef - Torres Strait region was performed.

The Inner Route is associated with many navigational hazards including strong tidal currents, underwater obstructions, narrowness of passageways and large amounts of recreational and fishing traffic (AMSA 1993). Additionally, it is characterised by seasonal weather changes and long on-duty times (AMSA 1993). Hence, the demands placed on pilots when navigating vessels along this route, are considerable and the fatigue potential high. For this reason the Australian Maritime Safety Authority have stipulated that at least 24 hours of rest excluding travel must be taken by pilots prior to all Inner Route voyages (AMSA 1997).

Figure 5.13 shows the mean duration of breaks between work assignments on the Inner Route. Table 5.7 summarises the analysis of Company and period differences in this data. Company C do not operate on this route and were therefore excluded from the present analysis. Breaks between Inner Route assignments were significantly longer for pilots from Company A (54.7 hours) compared with Company B (50.7 hours). This finding is consistent with the results of the previous section indicating shorter breaks between work assignments for Company B (Table 5.6).

The present result takes on additional significance when viewed in combination with the fact that Company B pilots perform 51% more work per 6 month period on the Inner Route (Section 5.3). Given the navigational demands and potential fatigue aspects of Inner Route voyages, the greater amount of work and shorter rest breaks experienced by Company B personnel may render this group more susceptible to acute and/or chronic fatigue development.

When examining the frequency distributions showing the duration of breaks between Inner Route passages (Figure 5.14a and Figure 5.14b), it is evident that in the majority of situations at least 24 hours rest is achieved, thereby meeting current rest break regulations. However, there were a number of situations when less than 24 hours rest was achieved. These situations represent an extremely limited opportunity for complete recovery between work assignments and should be carefully monitored if fatigue development is to be avoided.

Differences across time in mean duration of breaks between Inner Route assignments were evident, with rest breaks taken in the second period being significantly shorter (47.5 hours) compared to breaks taken in the first period (56.1 hours). No clear distinction was obtained for the third period. The shorter breaks are consistent with the finding indicating that significantly greater amounts of work were performed on this shipping route during the busy second 6 month period (Table 5.7).

Figure 5.13 Mean duration of breaks (hours) between work assignments on the Inner Route by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.7 Analysis of the mean duration of breaks between work assignments on the Inner Route (1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. p < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01).

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.14a Frequency distribution - Duration of breaks between work assignments on the Inner Route - Company A

Figure 5.14b

Frequency distribution - Duration of breaks between work assignments on the Inner Route - Company B

5.9 Duration of Breaks between Work Assignments - Hydrographers Passage

All three pilotage companies operate on Hydrographers Passage. As stipulated by the Australian Maritime Safety Authority (1997), a minimum of 12 hours rest, excluding travel, is required prior to undertaking pilotage work on this shipping route.

The average duration of breaks between assignments on Hydrographers Passage for each company and time period are depicted in Figure 5.15. Table 5.8 shows the results of the analysis of this data in terms of Company and period differences. Average rest breaks for Company C (72.0 hours) were significantly longer than for Companies A (46.8 hours) and B (44.2 hours), which were similar. These results appear to be confirmed by the frequency distributions for each company (Figure 5.16a, Figure 5.16b and Figure 5.16c). The majority of Company C’s breaks were in excess of 3 days (Figure 5.16c) whereas most breaks for Companies A and B ranged between 24 and 48 hours (Figure 5.16a and Figure 5.16b respectively). Such a finding is consistent with the irregularity of Company C’s work and hence, greater delays between work assignments.

While none of the rest breaks taken by Company C failed to meet the Australian Maritime Safety Authority’s minimum rest regulations, there were a number of times when the rest breaks of Companies A and B did not comply. Breaks of less than 12 hours represent an extremely limited time for recovery between work assignments and hence, may carry an increased risk of fatigue development.

There were no differences in the duration of breaks between assignments on Hydrographers Passage across the three 6 month time periods (Table 5.8).

Figure 5.15 Mean duration of breaks (hours) between work assignments on the Hydrographers Passage by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.8 Analysis of the mean duration of breaks (hours) between work assignments on the (Hydrographers Passage 1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. p < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when main effects not significant.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.16a Frequency Distribution - Duration of breaks between work assignments on the Hydrographers Passage - Company A

Figure 5.16b

Frequency Distribution - Duration of breaks between work assignments on the Hydrographers Passage - Company B

Figure 5.16c

Frequency Distribution - Duration of breaks between Hydrographers Passage assignments - Company C

5.10 Duration of Breaks between Work Assignments - Great North East Channel

The Great North East Channel is a particularly shallow shipping route, with underkeel clearance falling to below 12 metres during low tide (AMSA, 1993). Accordingly, high levels of vigilance are required when guiding vessels through this region. As decrements in vigilance performance are a common consequence of fatigue (Brown 1994; Krueger 1989), it is important that pilots begin work assignments on this route fully recovered from any previous work periods. At present, a minimum of 12 hours rest excluding travel is required prior to undertaking work assignments in this region (AMSA, 1997).

Figure 5.17 shows the mean duration of breaks between assignments on the Great North East Channel for each company and time period separately. Table 5.9 summarises the analysis of company and period differences in this data. Company C does not operate in this region and were therefore excluded from the present analysis. There were no significant differences between Companies A and B over the three time periods with regards to mean break duration between work assignments. This is consistent with previous results indicating work availability on this route did not vary greatly between companies or over time, and further reinforces the suggestion that shipping work on the Great North East Channel is fairly stable.

When data for Companies A and B are presented as frequency distributions (Figure 5.18a and Figure 5.18b), markedly skewed distribution curves are observed thereby indicating that the majority of rest breaks were at least 24 hours in duration. However, a small number of rest breaks were shorter, and some failed to meet the 12 hour minimum rest requirements stated by the Australian Maritime Safety Authority. This finding is of concern given the limited opportunity for complete recovery and increased potential for fatigue-related decrements in vigilance performance which could arise from such short rest breaks.

Figure 5.17 Mean duration of breaks between work assignments on the Great North East Channel by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.9 Analysis of the mean duration of breaks between work assignments on the Great North East Channel (1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. p < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when main effects not significant.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.18a Frequency distribution - Duration of breaks between work assignments on the Great North East Channel - Company A

Figure 5.18b Frequency distribution - Duration of breaks between work assignments on the Great North East Channel - Company B

5.11 Duration of Work Assignments spent at Night

Evidence within the literature suggests that night work is associated with higher levels of fatigue (Akerstedt 1995; Luna et al. 1997) and a greater risk of accidents (Brown 1994; Folkard 1997; Mitler et al. 1988). Hence, as the primary focus of the current project was to examine the extent and nature of fatigue experienced by Great Barrier Reef pilots as a consequence of their work practices, an analysis of the amount of night time periods of ship time performed by this group was highly relevant.

In the present investigation, night time periods were calculated from the civil twilight hours in three areas of the Great Barrier Reef region averaged across 12 months (Table 3.0). Based on these calculations, ship time between the hours of 1818 and 0525 was classified as night work. In the present stage of the analysis, no attempt has been made to differentiate between time actually spent on the bridge and time spent away from the bridge resting. Specific information of this nature will be provided by the on ship log books.

When travel was incorporated into work assignment duration, there was a significant (p<0.0001) increase in the amount of ship time performed at night.

The mean duration of work assignments spent at night across each 6-month period, for each company separately is depicted in Figure 5.19, while Table 5.10 summarises the analysis of this data in terms of company and period differences. Significant differences between all of the companies existed. Post hoc analysis revealed that the duration of work assignments at night time was greatest for Company A (24.9 hours), least for Company C (7.2 hours), with Company B (22.8 hours) situated between these two extremes (Table 5.10). The similar, but statistically different figures recorded for Companies A and B, are consistent with the compatibility between these two companies in terms of their similar operational routes.

When the mean percent of work assignment (ship time) undertaken at night was assessed, significant between company differences were evident with Companies A and B recording figures of 53.4% and 53.7% respectively, whereas Company C recorded a figure of 45.4% (p<0.01). The frequency distributions showing the percentage of work assignments performed during night time hours for Companies A and B (Figure 5.20a and Figure 5.20b) appear to confirm this finding as both distributions show classical bell shaped curves indicating night time periods on the ship constituted between 40 and 60% of most assignments. The relatively short transit times associated with pilotage of Hydrographers Passage gives rise to the somewhat inconsistent distribution of night time hours evident in the data of Company C (Figure 5.20c).

In order to overcome the natural desire to sleep during nocturnal hours and maintain appropriate levels of arousal and performance, greater effort must be invested by the night worker (Costa, 1993; Meijman et al. 1993; Totterdell et al. 1995). Night work also displaces sleep from usual sleeping hours which in turn reduces quality and quantity of recovery sleep (Akerstedt, 1995; Folkard, 1996; TSB, 1997). These features associated with night work place additional strain upon workers, which may manifest as greater decrements in performance and well-being (Bohle & Tilley 1989; Meijman et al. 1993; Totterdell et al. 1995) and higher levels of fatigue (Akerstedt 1995; Luna et al. 1997). Hence, to ensure Great Barrier Reef pilots have the opportunity for complete recovery between work assignments, it may be appropriate to adjust the length of breaks following work assignments involving significant amounts of night work.

Across the 18 month analysis period, there were no significant differences in the duration of work assignments performed at night (Table 5.10). This finding was constant for all companies, and suggests that regular night work is a common feature of Great Barrier Reef marine pilotage. An important finding with respect to the focus of this project towards fatigue, is that a substantial proportion of a Great Barrier Reef pilots work on board ship occurs at night.

Figure 5.19 Mean duration (hours) of work assignments (ship time) spent at night, by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.10 Analysis of the mean duration (hours) of work assignments (ship time) spent at night (incorporating travel) (1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. p < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when main effect not significant.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.20a Frequency distribution - Percent of work assignment hours spent at night per period - Company A

Figure 5.20b

Frequency distribution - Percent of work assignment hours spent at night per period - Company B

Figure 5.20c

Frequency distribution - Percent of work assignment hours spent at night per period - Company C

5.12 Starting Times of Work Assignments

Pilotage work is largely dependant on shipping demands and tidal conditions and as a consequence, work schedules tend to be highly irregular (Berger 1983; Shipley 1978; Shipley & Cook 1980). As irregular work hours may contribute to a greater susceptibility of acute and/or chronic fatigue development, an analysis of the starting times of Great Barrier Reef pilotage work assignments and rest breaks was considered important.

Figure 5.21 shows the mean starting times of work assignments (ship time)for each company and across time periods separately. Table 5.11 summarises the analysis of company and period differences in this data. No significant differences between companies or over time were evident. For all three companies and each time period, an average assignment starting time of around 1200 hours was calculated.

When examining the distribution of starting times for work assignments (Figure 5.22a, Figure 5.22b and Figure 5.22c), some insight into the mean figures can be obtained. For each company and across the 18 month analysis period, the starting times of Great Barrier Reef pilotage work assignments were fairly evenly distributed across the 24 hour cycle; that is, no clearly distinctive peak in work assignment starting times existed. As a consequence of this even distribution, a figure approximately midway through the 24 hour cycle was attained when mean starting time of assignments was calculated.

That pilotage work assignment starting times were fairly evenly distributed over the 24 hour cycle is consistent with the 24 hour nature of the shipping industry and corresponds favourably with data reported elsewhere in the literature. The most common boarding times for English marine pilots included 1700, 0100, 1800 and 2200 hours (Shipley 1978; Shipley & Cook 1980), while Port Phillip sea pilots begin work at all times throughout the 24 hour cycle (Berger 1983). It would therefore appear that the high level of irregularity associated with pilotage work is a common feature of all pilotage regions.

Irregular work hours create strain for workers in three ways (Monk 1989; Monk & Folkard 1992). Firstly, humans are diurnal creatures whose circadian rhythms have become entrained by the presence of social and environmental time cues to maximise wakefulness and arousal during the day and induce sleep at night. When required to work at times which conflict with the natural rhythms of the body, circadian dissociation may be experienced (Griffiths 1993; Luna 1997; Rosekind et al. 1996; Scott & Ladou 1990; TSB 1997). This in turn induces a sub-optimal psychophysiological state (de Vries-Grier & Meijman 1997) which may manifest as increased fatigue, mood deterioration and performance decrements (Condon et al. 1988; Griffiths 1993; Monk 1989; Monk & Folkard 1992; Rosekind et al. 1996).

Secondly, irregular work hours frequently displace sleep from normal sleeping hours thereby causing reductions in both quantity and quality of sleep. When sleep onset occurs after midnight, there is a progressive shortening of sleep length, such that a morning to noon bedtime culminates in around 4 to 4.5 hours of sleep (Akerstedt 1995; Folkard 1996). Additionally, sleep taken at times inconsistent with normal human physiology alters sleep composition and diminishes the recuperative value of sleep (Akerstedt 1995; Kecklund et al. 1997; Tilley et al. 1982; TSB 1997). As a consequence, fatigue, mood and performance may be adversely affected (Akerstedt 1995; Kecklund et al. 1997; Krueger 1989; Luna 1997; TSB 1997).

Thirdly, irregular work hours can create a plethora of social and domestic problems for the worker and his/her family (Monk 1989; Monk & Folkard 1992). Work and leisure times are often misaligned from society norms thereby interfering with the person’s ability to make regular contact with friends and family (Knauth & Costa 1996), and severely limiting the worker’s ability to plan ahead and organise personal, family and social events (Monk 1989; Monk & Folkard 1992).

These three areas are interrelated and as a consequence, strain in any one area can significantly affect the worker’s coping ability (Monk 1989; Monk & Folkard 1992). That Great Barrier Reef pilots experience such irregular work hours is therefore an important consideration when examining the potential fatigue impact of the work practices of this group.

Figure 5.21

Mean starting times of work assignments, by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.11 Analysis of the mean starting times of work assignments (incorporating travel) (1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. P < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when no significant main effect.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.22a Frequency distribution - Starting times of work assignments per period - Company A

Figure 5.22b

Frequency distribution - Starting times of work assignments per period - Company B

Figure 5.22c

Frequency distribution - Starting times of work assignments per period - Company C

5.13 Starting Times of Breaks between Work Assignments (incorporating travel to and from the ship)

Breaks between work assignments potentially provide pilots with an opportunity to recover from their previous work assignment and to prepare for their next. It is therefore desirable that the conditions experienced by pilots when ashore between voyages are conducive to maximising recovery. As time of sleep onset is an important factor in the recuperative value of sleep (Akerstedt 1995; Folkard 1996; Tilley et al. 1982; TSB 1997), an analysis of the most common starting times of the rest breaks between work assignments was undertaken.

The average starting times of rest breaks between work assignments for each company and time period are presented in Figure 5.23. A summary of the analysis of company and period differences in this data are shown in Table 5.12. Significant differences between companies and time periods did not exist. All companies and each time period recorded an average rest break starting time of around 1200 hours. This is once again attributable to the fairly even distribution of rest break starting times across the 24 hour cycle, as depicted by Figure 5.24a, Figure 5.24b and Figure 5.24c.

That pilotage work is so irregular is somewhat disconcerting, given the need for pilots to maximise recovery during their breaks between work assignments. In many situations it would appear that pilots are beginning their rest breaks and starting pilotage assignments at times which limit their opportunity for good recuperation. Sleep would frequently be displaced from normal sleeping hours and hence, the quality and quantity of the pilot’s sleep would most likely be compromised (Akerstedt 1995; Kecklund et al. 1997; Tilley et al. 1982; TSB, 1997). Additionally, pilots are often required to spend their recovery periods in alternative accommodation which may not always be conducive to optimising recovery (Rosekind et al. 1996; TSB 1997). Hence, if pilots are to achieve complete recovery between work assignments, it is important that the work hours and opportunities for maximum recovery are carefully monitored.

Figure 5.23 Mean starting times of breaks between work assignments by Company and period (incorporating travel), (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.12 Analysis of the mean starting times of breaks between work assignments (incorporating travel) (1 Jan 1996 - 30 June 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. P < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when no significant main effect.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.24a

Frequency distribution - Starting times of breaks between work assignments per period - Company A

Figure 5.24b

Frequency distribution - Starting times of breaks between work assignments per period - Company B

Figure 5.24c

Frequency distribution - Starting times of breaks between works assignments per period - Company C

5.14 Number of Potential Sleep Periods (2200-0800 hours) in Breaks between Work Assignments

There is a growing body of evidence within the literature suggesting that sleep beginning prior to midnight and spanning over the period when circadian alertness rhythms are low tends to be of superior recuperative value compared with fragmented or displaced sleep (Akerstedt 1995; Folkard 1996; TSB 1997). Hence, the time period spanning from ~ 2300 to 0700 hours could be considered optimal in terms of sleep recuperative value. As part of the present project, an analysis of the number of opportunities available to pilots to potentially achieve an uninterrupted block of sleep during this time period was undertaken. In consultation with a circadian rhythms and sleep expert, the time period was extended by 1 hour on either side (i.e. between 2200 and 0800 hours) to account for the time required to wind down and relax prior to sleep, and time required to overcome the effects of sleep inertia and prepare oneself for the upcoming day after waking (Personal Communication – Simon Folkard April 1998). Thus the present analysis examined the number of occasions during rest breaks between work assignments when the entire block of time from 2200 to 0800 hours was available to pilots.

Illustrated in Figure 5.25 are the mean number of potential sleep periods between 2200 and 0800 hours in breaks between assignments for each company and over the three time periods separately. Table 5.13 summarises the analysis of this data in terms of company and period differences. The opportunity to achieve an uninterrupted block of sleep during the optimal sleep period was significantly greater for Company C (2.5 potential opportunities), followed by Company A (1.80 potential opportunities) and then Company B (1.63 potential opportunities). Given that the more time off between work periods, the greater the probability that the 2200 to 0800 hour time period will be free, these results are consistent with the findings of section 5.7.

Findings within the literature have indicated that at least 2 nights of recovery sleep are required before complete recovery is achieved following a period of sleep deprivation (Dinges et al. 1997; Morris & Miller 1996; TSB 1997; Wittersheim et al. 1992). Thus, on average pilots from Companies A and B would have difficulty completely recovering from any sleep deprivation experienced during the preceding work period.

To further explore the number of opportunities for optimal sleep during rest breaks, Figure 5.26a, Figure 5.26b and Figure 5.26c present this data as frequency distributions. Evident from these figures is that approximately 40-60 percent of rest breaks between assignments provided less than 2 opportunities to achieve uninterrupted sleep between the hours of 2200 and 0800. This finding is of concern given that Great Barrier Reef pilots have reported compromised quantity and quality of sleep while working at sea (Parker et al. 1997).

The temporal analysis indicated that there was less opportunity available to achieve sleep during optimal circadian times during the second 6 month period. This result is consistent with the increased work availability previously noted during this time.

Figure 5.25 Mean number of potential sleep periods (2200 and 0800 hours) in breaks between work assignments by Company and period (1 Jan 1996 - 30 June 1997)

Note: Data analysis based on n values shown in Methods (Section 3.2).

Table 5.13 Analysis of the mean number of potential sleep periods (2200 and 0800 hours) in breaks between work assignments (Jan 1 1996 - June 30 1997) (1)

1. Results of full two-way analysis of variance (ANOVA) model including company and period effects. P < 0.01 considered statistically significant.
2. Results of Tukey’s Studentised Range Test for post-hoc differences (Type I Experimental Error Rate = .01) n/a Post hoc testing not performed when no significant main effect.

Company (Main Effect). This term measures whether or not there is a difference between companies averaged across the three time periods.

Period (Main Effect). This term measures whether or not there is a difference between the periods averaged across the companies.

Company * Period Interaction. This term measures whether or not the difference between the companies is the same in each period. Equally, it measures if the difference between periods is the same for each company. When the interaction is statistically significant there is little interest in the main effects. In this case averages over one of the factors ignore important variations.

Figure 5.26a Frequency distribution - Number of potential sleep periods (2200-0800 hours) in breaks between work assignments - Company A

Figure 5.26b Frequency distribution - Number of potential sleep periods (2200-0800 hours) in breaks between work assignments - Company B

Figure 5.26c

Frequency distribution - Number of potential sleep periods (2200-0800 hours) in breaks between work assignments - Company C

5.15 Summary

From the data presented in the preceding section, it is apparent that Company C personnel performed significantly fewer work assignments which were of shorter duration than either of the other two companies. These results reflect the single operational region of this company and the short transit time through Hydrographers Passage.

When comparing Companies A and B, in general pilots from Company B undertake more work assignments and experience shorter breaks between work assignments than pilots from Company A. The average duration of work assignments however, was slightly longer for pilots from Company A and as a consequence, the work to rest ratios calculated for the two pilot companies were the same. This finding suggests the operations of Companies A and B are similar.

Contrasting average work assignment duration and the work to rest ratios of Great Barrier Reef pilots with other groups of marine pilots revealed stark differences. Great Barrier Reef pilots undertake considerably longer work assignments than either Port Phillip sea pilots or long haul pilots from the United Kingdom, and experience much shorter rest breaks relative to work assignment duration compared with English long haul pilots. Therefore, it could be anticipated that as a consequence of their work conditions Great Barrier Reef pilots may be more susceptible to experiencing fatigue than some other groups of marine pilots.

Frequency distributions indicated that in some instances considerably greater workloads and shorter rest breaks were experienced by pilots, compared with mean company figures. These situations present a potentially heightened risk of acute and/or chronic fatigue development and therefore need to be carefully monitored.

In most situations, Great Barrier Reef pilots experience rest breaks of at least 24 hours duration between consecutive work assignments, thereby meeting the 12 and 24 hour minimum rest periods required prior to pilotage assignments. However there were a number of occasions on all shipping routes when less time was available and pilots from Companies A and B failed to meet current regulations. While extenuating circumstances may have existed on these occasions, the extremely limited opportunity for complete recovery between work periods associated with these short breaks is of concern with respect to the potential for fatigue. At no time during the 18 month analysis period did rest breaks between assignments for Company C fail to meet regulations.

Great Barrier Reef pilotage work is highly irregular and involves substantial amounts of night time periods on ships. That these parameters were stable over time and compared favourably with data from other groups of marine pilots suggests they are a common feature of pilotage work. Such work practices significantly impact on circadian rhythms, sleep and social and domestic factors, and may induce a sub-optimal psychophysiological state. As a consequence, there is the potential for increased levels of fatigue, mood deterioration and performance decrements.

Additionally, it was recognised that in approximately 10 to 20% of rest breaks between assignments, there was no opportunity for pilots to achieve an uninterrupted block of sleep between the hours of 2200 and 0800. As sleep taken outside this optimal zone tends to be inferior in terms of quantity and quality, the recuperative value of these rest breaks would most likely have been diminished.

In terms of changes across time, analysis of the number of work assignments per tour and per pilot, and the number of voyages performed on the Inner Route indicated significantly greater workloads during the second 6-month period (i.e. between July 1 1996 and December 31 1996). The increased workload across this period was primarily associated with the seasonal export of sugar from Queensland coastal ports. Additionally, the duration of breaks between work assignments on the Inner Route were significantly shorter during this time period. The same temporal pattern was observed for all of the pilot companies, thereby suggesting an increase in work availability during this period. The significant variations in the amount of pilotage work available across time more than likely contributes to the stress experienced by Great Barrier Reef pilots over job security and financial income, and for pilotage companies, complicates the process of distributing work equally between pilots and implementing appropriate fatigue management programs.

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